I was editing a student manuscript. The student remarked that it would be nice to see examples of quality writing in published work, and I realized that I couldn't really come up with good examples off the top of my head

What are the best examples of quality mathematical writing you've seen
?

Rules:

I'd prefer TCS papers as far as possible. Our style is different enough from standard math papers that I think it's better to focus on TCS (also why I'm asking here and not on MO)

it would help if you mentioned what exactly you thought the paper did well. Not all exposition is good at everything - some papers have great proof outlines, some use notation really effectively and others convey intuition masterfully.

if possible, please link to the paper.

I'm hoping this can become a resource, like many of our other broad questions. I'm marking it CW for that reason.

$\begingroup$Adding to Kaveh and Logan's comments, Don Knuth did a series of video lectures at Stanford based on the curriculum of "Mathematical Writing". I have the videos, but can't seem to find them hosted anywhere online. I wouldn't mind putting them up somewhere, but I'm sure there would be some copyright loop holes to jump through first.$\endgroup$
– Vincent RussoOct 15 '12 at 17:11

Except for the clear exposition, he nicely paints the bigger picture: why is any better-than-factor-of-2 approximation to MaxCut hard, why one would expect that spectral techniques could work, how his algorithm relates to Cheeger's inequality, and to the Goemans-Williamson SDP. In addition to the algorithm itself being very neat.

Oded Goldreich's In a World of P=BPP is one of the best written papers that I read. This is mostly due to the clarity of the exposition, the conceptual perspective, and the choice to include reflections regarding the meaning of the results in the paper.